Chocolate & Orange Zebra Cake aka Tiger Cake

Preheat oven to 180°C (356°F). Line baking tins with paper and brush with some of the melted butter. In one bowl beat the egg whites until stiff and leave aside. In second bowl place dry ingredients: flour, baking powder, sugar. Do not add cocoa powder yet. In small mixing bowl mix butter, oil, egg yolks, juice, vanilla extract, orange extract and zest, if using. Add them gradually to the bowl with dry ingredients and mix until well combined. Add also previously whisked egg whites. Move half of the dough into another bowl (same size) to combine with cocoa powder. If it is too thick (comparing to the yellow batter)… add a bit more juice. Leave the remaining half uncoloured. Pour some of the yellow cake batter into middle of each tin, then top with brown batter making sure it is more or less the same amount and it’s poured into the middle. Repeat those steps until no more ba...